Hair follicles, among other cells, are formed and maintained through the interaction between epithelium and dermis, and it has been shown that dermal papilla plays a key role in the growth of the hair follicle (Cohen J., J Embryol Exp Morphol. 9:117-27, 1961; Oliver R F., J Embryol Exp Morphol. 15(3):331-47, 1966; and Oliver R F., J Embryol Exp Morphol. 18(1):43-51, 1967). In hair follicles, the dermal papilla interacts with the outer root sheath to induce hair formation and growth, and to maintain the hair cycle consisting of anagen, catagen and talogen. When alopecia caused by inheritance, male hormones or stress progresses, the dermal papilla undergoes gradual degradation, resulting in the degeneration of hair follicles.
There are various forms of hair loss, including male- or female-type alopecia and alopecia areata. In the past, alopecia was treated typically by various methods of implanting artificial hair into hair follicle root bulbs of the scalp, but such artificial hair implant methods had led to some serious problems, and such methods are now banned. Currently, there are two methods employed to treat alopecia: drug or natural substance therapy, and human hair transplantation. The drug or natural substance therapy may retard the progress of alopecia or prevent future hair loss, but it may accelerate hair loss when the medication is stopped after a prolonged use. On the other hand, the transplantation of human hair involves taking plugs of natural hair from occipital hair growing areas and transplanting them to bald areas. Although the transplanted hair settles at the transplant area as a complete hair follicle and becomes a permanent hair that undergoes a normal growth cycle, the number of hair to be transplanted is severely limited, and in case of transplanting about 2,000 hair strands per one operation, it is generally not possible to perform more than three such operations. Thus, the methods currently used for treating alopecia have a number of limitations, and to overcome such problems, many researchers have attempted to revive hair follicles by in vitro culturing hair follicle cells and implanting them in the treatment area.
When dermal papilla cells isolated from hair follicle are cultured, they show a structure similar to fibroblast cells of the skin. Such cultured papilla cells have the ability to induce hair follicle formation, which is supported by the fact that the cells tend to aggregate during culturing. In other words, the dermal papilla cells at the initial phase of cultivation aggregate with each other, unlike fibroblast cells of the skin. However, said ability is not sustained indefinitely and Reynolds et al. have reported that when dermal papilla cells are cultured in vitro, they gradually lose their innate hair follicle-inducting ability after about 3 to 4 passage numbers (Reynolds A J et al., Development. 122 (10):3085-94, 1996). On the other hand, Jahoda and Reynolds et al. have reported that when dermal papilla cells of rat's vibrissa hair cultured 3 passage numbers or less are implanted into small ear skin wounds and the back of rats, abnormally large hair fibers displaying vibrissa hair-type characteristics emerge from the transplant sites (Jahoda C A., Development. 115(4):1103-9, 1992; and Reynolds A J. et al., Development. 115(2):587-93, 1992). The above reports suggest that the primary cultivation period of dermal papilla cells in vitro should be short and efficient in order to obtain a large number of the cells for transplantation.
Generally, the yield of the primary cultivation decreases with the age of the tissues or organs from which the cultured cells are obtained. Accordingly, researchers have turned their attention from differentiated cells to embryonic stem cells or adult stem cells for cell therapy for the re-growth of hair. For example, Kataoka et al. have reported that when floated cells obtained from a mixture of mesenchymal stem cells originated from bone marrow of a mouse and epithelial/dermal cells of a fetus are transplanted, the regeneration of skin with hair growth occurred and that specific markers for the transplanted mesenchymal stem cells have been found in hair follicles. This observation suggests that the mesenchymal stem cells may also be effective for hair re-growth. Further, Richardson et al. have reported that hair follicle dermal cells can be differentiated into adipocyte and osteocyte, and Martin et al. have reported that both mesenchymal stem cells originated from bone marrow and hair follicle dermal stem cells differentiate into osteocyte, chondrocyte, adipocyte and myocyte.
The present inventors have paid attention to the fact that mesenchymal stem cells originating from bone marrow, adipose tissue or umbilical cord have characteristics similar to the cells constituting dermal papilla and dermal sheath, and accordingly, have attempted to develop an effective method for in vitro re-constitution of dermal papilla tissues.